The present invention relates to a digital camera which has the function of capturing both still images and moving pictures.
Digital cameras generally mount an imaging element which outputs an original image signal of the object of imaging, a signal processing circuit which produces digital original image data on the basis of the original image signal output by the imaging element, an encoding circuit which compresses and encodes the original image data output from the signal processing circuit, and a memory circuit which stores the compressed encoded data output from the encoding circuit. In the encoding circuit, for example, the original image data is compression-encoded by means such as discrete cosine transformation, quantization, variable length encoding or the like. For instance, JPEG (Joint Photographic Coding Experts Group) is known as a standard using discrete cosine transformation, quantization, Huffman encoding or the like. Furthermore, for example, motion JPEG is known as a standard for compression-encoding a plurality of images that are continuous in a time sequence according to the JPEG standard. Furthermore, for example, MPEG (Moving Picture Experts Group) is known as a standard for compression-encoding moving pictures consisting of a plurality of images that are continuous in a time sequence. I pictures (Intra Pictures) which are intra-frame encoded images, P pictures (Predictive Pictures) which are inter-frame encoded images and B pictures (Bidirectionally Predictive Pictures) which are bidirectionally predictive encoded images are used in MPEG image compression.
As the performance of digital cameras has improved, digital camera models that have the function of taking both still images and moving pictures have been developed. In such digital camera models, the following function is provided: namely, typical frames are selected from the plurality of frames making up the moving pictures that are taken by the digital camera, and these frames are handled as still images. A technique for simplifying the determination of representative frames that reflect the intentions of the photographer is proposed in Japanese Patent Laid-open No. 2004-120403. In the same reference, the imaging section of the digital camera transmits the respective frames obtained by continued imaging of the object of imaging to a ring buffer in the order of image acquisition. The ring buffer stores the transmitted frames in the order in which these frames are received. When the shutter switch is depressed during imaging, a tag information producing section creates representative frame discriminating information which indicates that the frame imaged while the shutter switch is depressed are representative frames. After a specified time has elapsed from the depression of the shutter switch, the image data creating section prepares each representative frame stored in the ring buffer and a plurality of frames preceding and following the imaging of this representative frame as one set of image data, and attaches representative frame discriminating information.